chapter 5: light - fizikrahmahsamuri.net/light.pdfphysics module form 4 chapter 5 light 2 exercise...
TRANSCRIPT
Physics Module Form 4Chapter 5 Light
1
CHAPTER 5: LIGHT
In each of the following sentences, fill in the bracket the appropriate word or words given below.
solid, liquid, gas, vacuum, electromagnetic wave, energy
1. Light is a form of ( ).2. It travels in the form of ( )3. In can travel through ( )4. It travels fastest in the medium of ( )5. Light of different colours travels at the same speed in the medium of ( )
Light allows us to see objects.Light can be reflected or refracted.
5.1 UNDERSTANDING REFLECTION OF LIGHT
Plane mirror and reflection: In the boxes provided for the diagram below, write the name of eachof the parts indicated.
HUKUM PANTULAN/Laws of Reflection: Hukum Pantulan Cahaya menyatakan / State thelaws of reflection.
(i) …………………………………………………………………………………………….
………………………………………………………………………………………..……
(ii) ……………………………………………………………………………………………..
……………………………………………………………………………………………..
Plane mirror
Incident ray Reflected ray
Normal Reflected angleIncident angle
Point of incidence
i r
i r
Cermin Satah Planemirror
energyElectromagnetic waveSolid, liquid, gas and vacuum
vacuumvacuum
The incident ray, the reflected ray and the normal to the point of incidence, all lie in
the same plane./Sinar tuju,sinar pantulan,normal pada titik tuju berada pada satahyang sama
Sudut tuju i /The angle of incidence, i = Sudut Pantulan r / The angle of reflection, r
i=r
Physics Module Form 4Chapter 5 Light
2
Exercise 1. The diagram below shows how the relationship between incident angle and reflectedangle can be investigated.Fill in the values of the angles of reflection, r in the table below
Exercise 2:
Exercise 3:
OFFON
i r
OFF
ON
i r
i r10 1020 2030 3040 4050 50
Cermin/mirror
Cermin/mirror
Laser pen
Laser pen
Mirror
50o
o
normal
Original direction
d = 40o
d =40o +40o=80o
Mirror beforerotation
Cermin diputar o
/ Mirror rotated o
Reflected ray after rotation/sinaran pantulan selepasputaran
Incident raySinar tuju
Reflected ray beforerotation/sinar pantulan sebelumnormal
Physics Module Form 4Chapter 5 Light
3
Imej Cermin Satah /Image formed by a plane mirror: Using the law of reflection, complete theray diagram to determine the position of the image.
What can you say about the line joining object and image? ………………………………………
What can you say about the distances AB and BC? ………………………………………………..
Differences between real and virtual image:
Characteristics of image formed by plane mirror: Observe the pictures below as well as usingprevious knowledge, list the characteristics.
mirror
object image
i) virtual
ii) laterally inverted
iii) same size as object
iv) object distance =image distance
object
i1
r1
A B C
Eye
Image
Real image Virtual image
Can be caught on a screen Cannot be caught on ascreen
Formed by the meeting ofreal rays.
Form at a position whererays appear to be
originating.
Perpendicular to the mirror/berserenjangdengan cermin
AB = BC
Physics Module Form 4Chapter 5 Light
4
Exercise 1:
Exercise 2:
Exercise 3:
ACTIVITY: Find out some of the uses of plane mirrors (application of reflection).
Complete the ray diagram below consisting of 2 rays originating from the object, reflectedand entering the eye such that the eye sees the image.
objectEye
Mirror
Ahmad is moving with speed 2 m s-1 towards a plane mirror. Ahmad and his image willapproach each other at
A. 1 m s-1
B. 2 m s-1
C. 3 m s-1
D. 4 m s-1
Four point objects A, B, C and D are placed in front of a plane mirror MN as shown. Between theirimages, which can be seen by the eye?
M N
A B C DEye
image Dimage Cimage Bimage A
Only image D can be seen because the line joining image D to the eye cuts theactual mirror
Physics Module Form 4Chapter 5 Light
5
Curved Mirrors:
Terminology: Refer to the diagrams above and give the names for the following:
Effect of curved mirrors on incident rays:
a) Incident rays parallel to the principal axis:
Study the diagrams above and fill in the blanks for the following sentences.
r = 2f
PC
r
Concave mirror
C
r
P
Convex mirror
C = Centre of curvature
r = Radius of curvature
P = Pole
PC = Principal axis
Concave mirror Convex mirror
PC
r
f
F CP
r
F
f
Rays parallel to the principal axis converge at the ……………………, F F is positioned at the ………………….. between C and P FP is named the ………………………… which is denoted by f.
Hence write an equation giving the relationship between r and f.
Principal focusMid point
Focal length
Physics Module Form 4Chapter 5 Light
6
b) Incident rays parallel to each other but not parallel to the principal axis:
Study the diagrams above and fill in the blanks in the following sentences.
Parallel rays converge at a point called ……………………………
The focal plane joins F, the principal focus and all …………………………..and is
………………………. to the principal axis
The ray passing through C is reflected back along the line of the…………………….ray.
The distance between the focal plane and the mirror is the ………………………….,f.
Image formed by curved mirror (ray diagram method)
Principle of drawing ray diagrams:
a. Rays parallel to the principal axis are reflected through the principal focus, F.
PC
r
f
F
Focal plane
CP
r
F
f
Focal plane
Concave mirror Convex mirror
PC F P CF
Concave mirror Convex mirror
secondary focus
secondary foci
perpendicular
incident
focal length
Physics Module Form 4Chapter 5 Light
7
Exercise 1: Complete the ray diagrams below:
b) Rays passing through the principal focus are reflected parallel to the principal axis.
Exercise 2: Complete the ray diagrams below:
c) Rays passing through the center of curvature are reflected directly back.
PC F P CF
Concave mirror Convex mirror
PC F P CF
Concave mirror Convex mirror
PC F P CF
Concave mirror Convex mirror
PC F P CF
Concave mirror Convex mirror
Physics Module Form 4Chapter 5 Light
8
Exercise 3: Complete the ray diagrams below:
Image formed by concave mirror:
Using the principles of construction of ray diagram, complete the ray diagrams for each of the casesshown below:
u = object distance ; v = image distance ; f = focal length ; r = radius of curvature
Case 1: u > 2f
Hence state the characteristics of image formed:
i) ii) iii)
Case 2: u = 2f or u = r
Characteristics of image formed:
i) ii) iii)
C F Fobject
Concave mirror
image
PC F PC
F
Concave mirror Convex mirror
C Fimage
Fobject
Concave mirror
diminished real inverted
Same size real inverted
Physics Module Form 4Chapter 5 Light
9
Case 3: f < u < 2f
Characteristics of image formed:
i) ii) iii)
Case 4: u = f
Characteristics of image formed:
i)
Case 5: u < f
Characteristics of image formed:
i) ii) iii)
C F Fobject
Concave mirror
image
C F F
objectConcave mirror
C F F
objectConcave mirror
image
magnified real inverted
Image at infinity
magnified virtual upright
Physics Module Form 4Chapter 5 Light
10
Image formed by convex mirror: (using construction of ray diagram).
u = object distance ; v = image distance ; f = focal length ; r = radius of curvature
Characteristics of image formed:
i) ii) iii)
Uses of curved mirrors:
Newton’s Telescope: Fill in the boxes the type of mirror used
Activity: Find more uses of curved mirrors.
C F F
objectConcave mirror
image
Concave mirror
Plane mirror
Eye
Lens
ONOFFWhere should the lamp be placed to achieve theabove result? At the principal focus
Car head lamp Curved mirror
lamp
Diminished/ smaller size virtual upright
Physics Module Form 4Chapter 5 Light
11
5.2 UNDERSTANDING REFRACTION OF LIGHT
What is the phenomenon which causes the bending of light in the picture above?
…………………………………………………………………………………………………………
Why did this bending of light occur? (think in terms of velocity of light)
…………………………………………………………………………………………………………
Refraction of light:Fill in each of the boxesthe name of the part shown
air
water
i
i
r
r
GlassAir
Air
refraction
The velocity of light changes when it travels from one medium into another
Incident rayIncident angle Normal
Refracted angle
Refracted ray
Emergent angleEmergent ray
Physics Module Form 4Chapter 5 Light
12
Direction of refraction:
Draw on the diagrams above the approximate directions the refracted rays.
When light travels from a less dense medium to a denser medium, the ray is refracted(toward/away from) the normal at point of incidence.
When light travels from a more dense medium to a less dense medium, the ray is refracted(toward/away from) the normal at point of incidence.
Snell’s law:
Snell’s law states that ……………………………………………………
What is the name and symbol of the constant? …………………………..
Exercise 1:
Referring to the diagram on the right,Calculate the refractive index of liquid-X.
0
0
30sin60sin
n
= 1.732
Air
Liquid-X
60o
30o
Less densemediumDensermedium
densermedium
Less densemedium
normal normal
The ratio of sin(angle of incident) to sin(angle of refraction) is aconstant
i.e. constant
sinsin
anglerefractedangleincident
Refractive index, n
n1 sin i = n2 sin r
Physics Module Form 4Chapter 5 Light
13
Exercise 2:
Referring to the diagram on the right,Calculate the refractive index of liquid-Y.
n = 1.414
Exercise 3:
On the diagram to the right, draw two rayswhich originate from the fish to showhow a person observing from abovethe surface of the water is able to see theimage of the fish at an apparent depthless than the actual depth of the fish.
Exercise 4:An equation that gives the relationship between apparent depth, real depth and the refractive indexof water for the diagram above is
depthapparentdepthreal
n
If the fish is at an actual depth of 4 m and the refractive index of water is 1.33, what is the apparentdepth of the image?
Apparent depth = 3 m
Air
water
Eye
Air
Liquid-Y
45o
30o
object
image
Physics Module Form 4Chapter 5 Light
14
5.3 UNDERSTANDING TOTAL INTERNAL REFLECTION OF LIGHT
Critical angle and total internal reflection:
Figures a, b and c show rays being directed from liquid-Y which is denser than air towards the airat different angles of incident,.
Among the figures a, b and c, only Figure ahas a complete ray diagram.
(i) Complete the ray diagrams forFigure b and Figure c.
(ii) The angle, C is called …………………….
(iii) The phenomenon which occurs inFigure c yang is called
…………………………………….
(iv) State 2 conditions which must be satisfied in order for the phenomenonyou mentioned in (iii) to occur.
………………………………………………………………………………………
………………………………………………………………………………………
Exercise 1:
Referring to figure d and using Snell’s law,write an equation that gives the relationshipbetween the critical angle, C, the refracted angleand the refractive index of liquid-Y
Cn
sin1
Air
Liquid-Y
< C
Figure a
Air
Liquid-Y
90o
C
Figure b
AirLiquid-Y
> C
Figure c
Air
Liquid-Y
90o
C
Figure d
Critical angle
Total internal reflection
Light must travel from denser medium to less dense medium
The angle of incident must be greater than the critical angle
Partial reflection
Total reflection
Physics Module Form 4Chapter 5 Light
15
Exercise 2:
Referring to Figure e, determine therefractive index of liquid-Z
030sin1
n
= 2
Exercise 3:
Explain why a pencil partially immersed in water looks bent.(Use a ray diagram).
Exercise 4:
Complete the path of the ray in the diagram below and explain how a mirage is formed.
During the day, the ground is heated by the sun. The layer of air near the ground is hotter than thelayers above. Hot air is less dense than cool air. Therefore ray from object is refracted away fromthe normal. When angle of incident becomes larger than the critical angle, total internal reflectionoccurs. Thus a mirage is formed.
Air
Liquid-Z
90o
30o
Figure e
Eye
image
Layer of hot air
Layer of cool air
Eye
object
ground
Image(mirage)
i > C
Physics Module Form 4Chapter 5 Light
16
Exercise 5:
Completing the ray diagram below, to show how a periscope works: (critical angle of glass = 42o)
Eye
Glass prismObject45o
Total internalreflection takesplace because angleof incident > criticalangle
Physics Module Form 4Chapter 5 Light
17
5.4 UNDERSTANDING LENSES
Thin Lenses :
Types of lenses : Name the types of lenses shown below.(i)
(ii)
Formation of a convex lens and terminology: name the parts shown
Formation of a concave lens and terminology: name the parts shown
a. Biconvex b. Plano-convex c. Convex meniscus
a. Biconcave b. Plano-concave c. Concave meniscus
Principal axis
Centre of curvature
Optic centre,O
Optic centre
Principal axis
Centre of curvature
Physics Module Form 4Chapter 5 Light
18
Refraction of rays parallel to the principal axis of a convex lens:
Draw in the following diagrams the paths of the rays after passing through the lens.Write in the boxed provided, the name of the point or line shown.
i)
ii)
iii)
iv)
Focal plane
Secondary focus
Principal focus
Principal focus
Focal plane
Secondary focus
F
F
F
F
Physics Module Form 4Chapter 5 Light
19
Principles of constructing ray diagrams: Complete the path of each ray after passing through thelens
i) ii) iii)
iv) v) vi)
vii) viii)
Exercise 1:
State the meaning of each of the following terms:
i) Focal length , f : The distance between optic centre and the principal focus (OF)
ii) Object distance, u : The distance between the object and optic centre
iii) Image distance, v : The distance between the image and the optic centre
Exercise 2:
Describe how you would estimate the focal length of a convex lens in the school lab.
Place the lens facing the window on the far side of the lab. Adjust the distance of a screen behindthe lens until a sharp image of the window is formed. Measure the focal length (distance betweenthe lens and the image).
FF
FF
FF
FF
FF
FF
FF F
F
Physics Module Form 4Chapter 5 Light
20
Characteristics of image formed by a convex lens : (Construction of ray diagram method)
Construct ray diagrams for each of the following cases and state the characteristics of the imageformed.
i) Case 1 : u > 2f where u = object distance ; and f = focal length of lens.
Characteristics of image:
Diminished(smaller size), real and inverted
ii) Case 2 : u = 2f
Characteristics of image:
Same size, real and inverted
iii) Case 3 : 2f > u > f
Characteristics of image:
Magnified(bigger size), real and inverted
F
F
2F
object
Lens
F
F
2F
object
Lens
F
F
2F
object
Lens
image
image
image
Physics Module Form 4Chapter 5 Light
21
iv) Case 4 : u = f
Characteristics of image:
Image at infinity
v) Case 5 : u < f
Characteristics of image:
Magnified, virtual, upright
Exercise:
In each of the following statements below, fill in the space provide one of the following conditions.( u > 2f / 2f = u / 2f > u > f / u > f / u < f )
i) To obtain a real image, the object must be placed at a distance u such that … u > f ………
ii) To obtain a virtual image, the object must be placed at a distance u such that u < f ………
F
F
2F
object
Lens
2F
object
Lens
F
F
image
Physics Module Form 4Chapter 5 Light
22
Characteristics of image formed by concave lens : (by construction of ray diagrams )
Construct a ray diagram for each of the following and state the characteristics of the image formed
i)
Characteristics of image:Diminished, virtual, upright
ii)
Characteristics of image :Diminished, virtual, upright
Note: Image formed by a concave lens is always diminished, virtual and on the same side of thelens as the object.
Power of a lens (p)The power of the lens is given by:
Power of lens =lengthfocal1
Sign convention (for focal length) and the S.I. unit for power of a lens. The focal length of a convex lens is (positive/negative) The focal length of a concave lens is (positive/negative) The S.I. unit for the power of a lens is…Dioptre…and its symbol is…D… When calculating the power of a lens, the unit of the focal length must be in (m/cm)
Exercise 1 : A concave lens has a focal length of 10 cm. What is its power?
fp
1 =
1.01
= -10 D
F
F
2F
object
Lens
F
F
2F
object
Lens
image
image
Physics Module Form 4Chapter 5 Light
23
Exercise 2 : The power of a lens is + 5 D. State whether it is a convex lens or a concave lens andcalculate its focal length.
Convex lens.
f = 20 cm
Linear Magnification (m) :
Definition: Linear magnification =ceobjectdisceimagedis
tantan
objectofheightimageofheight
uv
hhm i
0
Based of the definition above and the ray diagram below, derive an expression for the relationshipbetween linear magnification, m, the object distance, u and the image distance, v.
The triangles, ABO and DCO are similar triangles.
Therefore,uv
hhi
0
Therefore,uvm
Lens formula :
The relationship between the object distance, u, image distance, v, and the focal length, f, of a lensis given by
fvu111
This lens formula is valid for both convex and concave lenses.
When using the lens formula, the ‘real is positive sign convention’ must be followed.
The rules stated in this sign convention are:
v
hi
u
ho
Lens
A
B
O C
D
Physics Module Form 4Chapter 5 Light
24
1) The focal length of a convex lens is positive while the focal length of a concave lens is negative
2) Object distance is positive for real object; object distance is negative for virtual object
3) Image distance is positive for real image: image distance is negative for virtual image
Application of the lens formula:
Exercise 1. An object is placed 10 cm in front of a converging lens of focal length 15 cm.Calculate the image distance and state the characteristics of the image formed.
fvu111
1511
101
v
101
1511
vv = - 30 cmImage is virtual
Exercise 2 : An object is placed 30 cm in front of a converging lens of focal length 25 cm.a) Find the position of the image, and state whether the image is real or virtual.b) Calculate the linear magnification of the image.
2511
301
v
v = 150 cm ; Image is real
m = v/u
m = 150/30
m = 5
Latihan 3 : An object is placed 30 cm in front of a diverging lens of focal length 20 cm. Calculatethe image distance and state whether the image is real or virtual.
2011
301
v
v = - 12 cm ; image is virtual
Physics Module Form 4Chapter 5 Light
25
Lenses and optical instruments :
1. Magnifying glass (simple microscope ):
A lens acts as a magnifying glass when the object is placed as in case 5 on page 23.
i) A magnifying glass consists of a (converging / diverging) lens.ii) The object must be placed at a distance (more than f / same as f / less than f / between
f and 2f / more than 2f) in order for the lens to act as a magnifying glass.iii) The characteristics of the image formed by a magnifying glass are yang (real / virtual) ;
(inverted / upright) ; (magnified /diminished) ; (on the same side as the object / onthe opposite side of the object).
iv) Greater magnification can be obtained by using a lens which has (long / short) focallength.
Complete the ray diagram below to show how a magnifying glass produces an image of theobject.
Exercise 1 : A magnifying glass produces an image with linear magnification = 4. If the power ofthe lens is +10 D, find the object distance and image distance.
uv4 uv 4
f110 10 f cm
101
411
uu5.12u cm
v = 50 cm
Exercise 2: Which of the following lenses with their powers given below makes the magnifyingglass with the highest power of magnification?
A. – 5 D B. –25 D C. +5 D D. +25 D.
2F
object
Lens
F
F
image
Physics Module Form 4Chapter 5 Light
26
2. Simple camera : The diagram below shows the structure of a simple camera. In the boxesprovided, write the names of the parts shown.
For each of the parts you have named, state its function.
Lens: to focus a sharp image onto the filmFilm: to record the imageDiaphragm: to adjust the size of the aperture (control the brightness of image).Shutter: to open and shut the camera so that the film is exposed only for a short time.
3. Slide projector : The diagram below shows the structure of a simple camera. In the boxesprovided, write the names of the parts shown
Complete the ray diagram above to explain how the slide projector works.
Diaphragmadjustment ring
Focusingscrew
Film drum
CondenserConcavemirror
Lightsource
slide
Projectorlens
Screen
Lens
Film
Shutter
Diaphragm
Physics Module Form 4Chapter 5 Light
27
4. Astronomical telescope :
Making of the astronomical telescope.
The astronomical telescope consists of 2 (converging / diverging) lenses. The objective lens has focal length, fo and the eye lens has focal length, fe where ( fo < fe
/ fo > fe ). The lenses are arranged such that the distance between the objective lens and the eye
lens is (fo – fe / fo + fe / fo x fe / fo/fe).
Complete the ray diagram above to show how the astronomical telescope works.
Characteristics of image formed by an astronomical telescope:
The first image formed by the objective lens is (virtual/real ; upright/inverted ;diminished/magnified).
The final image is (virtual/real ; upright/inverted ; diminished/magnified).
The final image is located at ( Fo / Fe / infinity).
Magnifying Power (M) :
M =ff
e
0
Exercise:
An astronomical telescope with high power of magnification can be built using eye lens of (long /short) focal length and objective lens of (long / short) focal length.
Parallel raysfrom distantobject Objective lens
FeFo
Eye lens
Image atinfinity
Physics Module Form 4Chapter 5 Light
28
5. The compound microscope :
Structure of the compound microscope:
A compound microscope consists of 2 (converging / diverging) lenses The focal length of the eye lens is (long / short) and the focal length of the objective lens is
(long / short). The objective lens is arranged such that the object distance, u is (u = fo / fo < u < 2 fo / u
=2fo). The eye lens is used as a (magnifying / diverging / projector) lens. The total length, s, between both lenses is ( s = fo + fe ; s > fo+fe )
Complete the ray diagram above to show how the compound microscope works.
Characteristics of image formed by compound microscope:
The first image formed by the objective lens is (real/virtual ; diminished/magnified ;upright/inverted ).
The final image is (real/virtual ; diminished/magnified ; upright/inverted ).
Exercise 1 (a) : A compound microscope consists of two lenses of focal lengths 2 cm and 10 cm.Between them, which is more suitable as the eye lens? Explain your answer.
The 10 cm lens is used as the eye lens because it will make a shorter microscope.
(b): How would you arrange the lenses in (a) to make an astronomical telescope?
Use the 10 cm lens as the objective lens and the 2 cm lens as the eye lens.
Object
L0
FeFo
LeEye
Image2
Physics Module Form 4Chapter 5 Light
29
Reinforcement:Part A:
1. Between the following statements about reflection of light, which is not true?
A. All light energy incident on a plane mirror is reflected.B. The angle of incidence is always the same as the angle of reflection.C. The incident ray, the reflected ray and the normal to the point of incidence, all lie on the
same plane.D. The speed of the reflected ray is the same as the speed of the incident ray.
2. A boy stands in front of a plane mirror. He observes the image of some letterings printed on hisshirt. The letterings on his shirt is as shown in Figure 1.
Between the following images, which is the image observed by the boy?
3. Figure 2 shows an object, O placed in front of a plane mirror. Between the positions A, B, Cand D, which is the position of the image?
4. A student is moving with a velocity of 2 m s-1 towards a plane mirror. The distance betweenthe student and his image will move towards each other at the rate
A. 2 m s-1 B. 3 m s-1 C. 4 m s-1 D. 5 m s-1 E. 6 m s-1
5. The table below shows the characteristics of the images formed by a concave mirror for variouspositions of the object. All symbols used have the usual meanings. Which of them is not true?
Position of object Characteristics of imageA u > 2f Diminished, inverted, realB f < u < 2f Magnified, inverted, realC u = f Same size, inverted, realD u < f Maginfied, upright, virtual
Figure 1
A B C D
O
A B C D
Plane mirror
Figure 2
Physics Module Form 4Chapter 5 Light
30
6. Which of the following ray diagram is correct?
7. The depth of a swimming pool appears to be less than its actual depth. The light phenomenonwhich causes this is
A. ReflectionB. RefractionC. DiffractionD. Interference
8. The critical angle in glass is 42o. What is the refractive index of glass?
A. 1.2 B. 1.3 C. 1.4 D. 1.5 E. 1.6
9. Which of the following are the characteristics of an image formed by a magnifying glass?
A. Magnified, virtual, invertedB. Diminished, real, uprightC. Magnified, virtual, uprightD. Diminished, virtual, inverted
10. A student is given three convex lenses of focal lengths 2 cm, 10 cm and 50 cm. He wishes toconstruct a powerful astronomical telescope. Which of the following arrangements should hechoose?
Focal length of objective lens / cm Focal length of eye lens / cmA 50 2B 10 10C 2 50D 50 10
50o
50o
C F
Convex mirror
C F
Concave mirrorPlane mirror
A B C
Physics Module Form 4Chapter 5 Light
31
Part B
1.
Figure 3 shows the eye of a person looking at a fish.
a) Sketch a ray diagram consisting of 2 rays originating from the eye of the fish to show why theimage of the fish is seen closer to the surface.
b) The fish is at a depth of 2 m. If the refractive index of water is 1.33, calculate the apparentdepth of the fish.
depthapparentdepthreal
n
depthapparent233.1
Apparent depth = 1.5 m
2.
a) Starting with the lens formula,fvu111 , derive an equation that gives the relationship
between liner magnification, m and the image distance, v. Hence sketch the graph of m against v onthe axes provided below.
fv
vv
uv
fvm 1
11 v
fm
air
water
Eye
Figure 3
Image
Physics Module Form 4Chapter 5 Light
32
(b) State the value of m at the point of intersection of the graph with the vertical axis.
-1(c) Describe how you would determine the focal length of the lens using the graph.
The gradient of the graph gives the value of 1/f
Thereforegraphofgradient
1f
Part C1.A student used a slide projector to project a picture onto the screen. Figure 1a and 1b show therelative positions of the slide, projector lens and the screen.It is observed that when the screen is moved further away (Figure 1b), the lens of the projector hasto be moved nearer to the slide to obtain a sharp image.
SlideScreen
image
Figure 1a
Figure 1b
Projectorlens
Projectorlens
Slide
Screen
image
0
m
v
-1
Physics Module Form 4Chapter 5 Light
33
Based on your observations and knowledge of lenses;a) make one suitable inference.The image distance is dependent on the object distanceb) state an appropriate hypothesis that could be investigated.
The greater the object distance, the smaller the image distancec) describe how you would design an experiment to test your hypothesis using a convex lens,
filament bulb and other apparatus.In your description, state clearly the following:(i) aim of the experiment
To investigate the relationship between object distance and image distance for a convex lens.(ii) variables in the experiment
Manipulated variable: object distance.Response variable: image distance.Fixed variable: focal length of lens.
(iii) List of apparatus and materialsApparatus: light bulb, convex lens of focal length 10 c , white screen, metre rule, low
voltage power supply and lens holder(iv) Arrangement of the apparatus
(v) The procedure of the experiment, which includes the method of controlling themanipulated variable and the method of measuring the responding variable
Procedure: 1. Arrange the apparatus as shown in the diagram above.2. Adjust the bulb so that the object distance (filament), u is 35 cm from
the lens.3. Light up the electric bulb, adjust the screen position until a sharp image
of the filament is formed on the screen. Record the image distance, v.4. Repeat steps 2 and 3 for objects distances of, u = 30cm, 25 cm, 20 cm,
and 15 cm.
(vi) The way you tabulate the data
Object distance,u /cm
Image distance,v /cm
35.030.0
Objectdistance
Imagedistance
bulb lens screen
Meter rule
Low voltage power supply
Lens holder
Physics Module Form 4Chapter 5 Light
34
25.020.015.0
(vii) The way you would analyse the dataPlot the graph of v against u
2.A student carried out an experiment to investigate the relationship between object distance, u,and image distance, v, for a convex lens. The student used various values of u and recorded thecorresponding values of v. The student then plotted the graph of uv against u + v as shown inFigure 2.
Figure 2
500
500450
400
35055
3000
250
2000
150
100
50
uv/ cm2
10 20 30 40 50u + v / cm
Physics Module Form 4Chapter 5 Light
35
a) Based on the graph in Figure 2,
(i) state the relationship between uv and u + v
…………………………………………………………………………………………[1 mark]
(ii) determine the value of u + v when the value of uv = 400 cm2. Show on the graph howyou obtained the value of u + v.
40 cmFrom the value of u + v obtained, calculate the image distance, v when u = 20 cm.
20 + v = 40v = 20 cm
[3 marks](iii) calculate the gradient of the graph. Show clearly on the graph how you obtained the
values needed for the calculation.
Gradient = 400/40= 10 cm
[3 marks]
b) Given that the relationship between u, v and focal length, f of the convex lens used, isrepresented by the equation
1 + 1 = 1u v f
Derive an equation which gives the relationship between uv and (u + v ).
fuvuv 1
vufuv
[2 marks]
c) Using the equation derived in (b), and the value of gradient calculated in (a)(iii), determine thefocal length of the lens used in the experiment.
The gradient = fTherefore f = 10 cm
[2 marks]
d) State one precaution taken to ensure the accuracy of the experiment.
………………………………………………………………………………………[1 mark]
uv is directly proportional to (u + v)
The object (lamp), lens and the screen must be arranged in a straight lineperpendicular to the screen